Hi JimEarly 4 wire Sprengbrock or possibly a Bonner. In the early days of RC they were the best (and dearest) available. Looks like this was wired to operate a change over switch and potentiometer. If it was in a boat it was possible used as a speed controller using transistors.

Hi DougThis site has always been a mine of info for early RC gear. I have built many of the suggestions and have a good supply of spares and motors for the Skyleader servos including the Ferranti chips.Servos are so cheap to buy today that it really isn't worth my time to build. Restoring an old set is enjoyable but I abandoned 27Mhz a few years ago and 40Mhz is going the same way unless you are into submersibles.I still have all my old books and mags on RC prior to the proportional era and it all seems so basic compared to what we have now.Dave

"and it all seems so basic compared to what we have now."Absolutely, but full of improvisation and ingenuity! And damn heavy!!I also built servos and ESCs in the past, but as you say it's not worth it now, especially for the micro versions I need for Plastic Magic. But I still build the odd control / switch / relay board for special functions. That's also fun, in a masochistic sort of way! I still keep my MC10 40Meg set going for the U26, even though I haven't managed to get it underwater yet 🤔 and an even older Sanwa / MacGregor 35Meg set for the odd plane / airship / flying boat still kicking around. variety is the spice of life 😉Cheers Doug 😎

Hi Guys, Cant agree more. the reliability etc was always suspect, sudden glitches were the death of several of my models, Just had our club guru convert my Macgregor IV to 2.4ghz using a Futaba module, he has done a Robbe F14 for me as well, I doff my cap to you electronics guys, i know its a basis of switching but changing batteries and a bit of soldering is my limitMark